1. Field of the Invention
The present invention relates to a projection lens unit mounted on a portable type ultra-small projector and projecting an image, which is formed by an image forming apparatus, on a screen.
2. Description of the Related Art
Recently, portable type electronic apparatus have come into wide use in which a light projector is incorporated into a personal computer, a mobile phone or a digital camera so that a projecting function can be added in addition to the original function of the electronic apparatus. Further, portable type ultra-small projectors, on which only the projecting function is mounted, have been on the market. There is a strong demand of reducing the sizes of the light projectors incorporated into those portable type electronic apparatus. Especially, a reduction of the thickness of the apparatus is the most important task. In general, when consideration is given to mounting a projection lens on a housing of the light projector, a size of the holding portion, on which a projection lens for projecting an image on a screen is mounted, is inevitably increased and becomes larger than the size of a lens barrel portion. Accordingly, this portion has a great influence on the size and thickness of the overall apparatus. For example, as shown in FIG. 6, the lens barrel portion is composed as follows. In an outer circumferential portion on the incident side of the projection lens barrel 50, the flange portion 53 having the mounting face 52, which is perpendicular to the lens optical axis 51, is provided so that the lens optical axis 51 of the projection lens barrel 50 can be maintained to be highly accurately perpendicular to the mounting face of the apparatus.
Since a plurality of lenses are incorporated into such a projection lens barrel, it is necessary to adjust a focus after the lenses have been incorporated. Further, such a problem may be caused that the focusing position is shifted because of rattling of the lens caused by the vibration in the process of conveyance. In preparation for the occurrence of such a problem, a structure, by which an adjustment can be easily made again, is disclosed in the following JP-A-2007-025579 and JP-A-2007-041157.